Echolocation

As we were heading to Karate last Monday, I was listening to Olivia and Zach play and interact in the car.  Imaginary play is a big part of what they do now and has been for a very long time.  Kitty cat, anyone? So they are playing with bats that I just bought them at Party City.  Hey, last year around this time, it was a huge, white rat that Olivia begged for (and got).  So, we are moving up with the bats, in my book. 
Zach comes out with "I can hear you with my echolocation".  Echolocation??!  This 4-year old is paying attention.  Dophins use echolocation and he's obviously heard this term before and knows how to use it.  Bats use echolocation as well, I Googled it.  The 4-year old is teaching me.